The present invention relates generally to leadframes for use in an integrated circuit package and more specifically to a particularly designed leadframe which prevents die pad shifting during the molding of the package, prevents delamination and cracking of the package, and provides an arrangement for electrically interconnecting multiple integrated circuit die attached directly to the leadframe without the use of an additional substrate or interfacing board.
In the field of integrated circuit packaging the cost of the components making up the package and the complexity of the manufacturing process are of major concern. Any improvement which simplifies the manufacturing process, improves the durability of the package, or reduces the cost of the components making up an integrated circuit package can provide a significant commercial advantage. Also, in order to reduce the amount of material required to produce a given package and reduce the space required by the finished integrated circuit package, packages are being made smaller and thinner. Because of these factors, the packaging of integrated circuits is continuously being improved to provide smaller more cost effective designs and methods for producing integrated circuit packages.
Referring initially to FIG. 1, a current prior art single chip integrated circuit package generally indicated by reference numeral 10 will be described. Package 10 includes a leadframe 12, a die attach pad 14, an integrated circuit die 16, and a molded encapsulant material 18 surrounding die attach pad 14, die 16, and portions of leadframe 12. Integrated circuit die 16 is typically attached to die attach pad 14 using a die attach adhesive and the die is typically electrically connected to leadframe 12 using an array of conventional bonding wires, one of which is indicated by reference numeral 22. On thin integrated circuit packages, die pad shift due to the injection of the encapsulant material during molding of the package is a common manufacturing problem. This is caused by uneven pressures generated above and below the die attach pad during the injection of the encapsulant material. Also, because of the small amount of cross sectional area of encapsulant material between the upper portion and the lower portion of the molding material (especially in the case of a large die attach pad), delamination of the mold compound from the leadframe is another manufacturing problem. The present invention provides a leadframe which eliminates these problems.
Referring to FIGS. 2A and 2B, two typical prior art multi-chip integrated circuit package designs generally designated by reference numerals 24 and 26 respectively will be described. Multi-chip package 24 includes a leadframe 28, a die attach pad 30, an interconnecting substrate 32, two integrated circuit die 34, and a molded encapsulant material 36 surrounding pad 30, substrate 32, die 34 and portions of leadframe 28. Die 34 are electrically interconnected and electrically connected to leadframe 28 using a combination of interconnecting substrate 32 and an array of bonding wires 38 . Typically interconnecting substrate 32 includes electrically conductive paths or traces (not shown) laid out to position bonding pads (also not shown) in appropriate locations for bonding wires 38 to complete the electrical interconnection of the two die 34. In the case of FIG. 2B, die attach pad 30 is eliminated and substrate 32 is attached directly to leadframe 28. In addition to having the problems described above for single chip packages, the described typical prior art multi-chip packages have the added disadvantage of the additional cost of the interconnecting substrate 32 which must include the required electrically conductive paths. Also, there is the additional manufacturing cost of attaching substrate 32 to die attach pad 30 or leadframe 28 depending on which of the described approaches is used. The present invention provides a leadframe which is used without an interconnecting substrate to interconnect the die, therefore eliminating the need for an interconnecting substrate and eliminating the need to attach the substrate to the leadframe.